Wholly aromatic polyester resins long have been known. For instance, p-hydroxybenzoic acid homopolymer and copolymers have been provided in the past and are commercially available. Those wholly aromatic polyesters normally encountered in the prior art have tended to be somewhat intractable in nature and to present substantial difficulties if one attempts to melt process the same while employing conventional melt processing procedures. Such polymers commonly are crystalline in nature, relatively high melting or possess a decomposition temperature which is below the melting point, and when molten frequently exhibit an isotropic melt phase. Molding techniques such as compression molding or sintering may be utilized with such materials; however, injection molding, melt spinning, etc. commonly have not been viable alternatives or when attempted commonly have been accomplished with difficulty. Such polymers commonly cannot be melt extruded to form nondegraded fibers. Even those wholly aromatic polymers which exhibit a melting point below their decomposition temperature commonly melt at such high temperatures that quality fibers may not be melt spun. For instance, fibers melt extruded at extremely high temperatures commonly possess a voidy internal structure and diminished tensile properties.
Representative publications which discuss wholly aromatic polyesters include: (a) Polyesters of Hydroxybenzoic Acids, by Russell Gilkey and John R. Caldwell, J. of Applied Polymer Sci., Vol. II, Pages 198 to 202 (1959), (b) Polyarylates (Polyesters From Aromatic Dicarboxylic Acids and Bisphenols), by G. Bier, Polymer, Vol 15, Pages 527 to 535 (August 1974), (c) Aromatic Polyester Plastics, by S. G. Cottis, Modern Plastics, Pages 62 to 63 (July 1975), and (d) Poly(p-Oxybenzoyl Systems): Homopolymer for Coatings: Copolymers for Compression and Injection Molding, by Roger S. Storm and Steve G. Cottis, Coating Plast. Preprint, Vol. 34, No. 1, Pages 194 to 197 (April 1974). See also, U.S. Pat. Nos. 3,039,994; 3,169,121; 3,321,437; 3,553,167; 3,637,595; 3,651,014; 3,723,388; 3,759,870; 3,767,621; 3,787,370; 3,790,528; 3,829,406; 3,890,256; and 3,975,487.
Also, it more recently has been disclosed that certain polyesters may be formed which exhibit melt anisotropy. See for instance, (a) Polyester X7G-A Self Reinforced Thermoplastic, by W. J. Jackson, Jr., H. F. Kuhfuss, and T. F. Gray, Jr., 30th Anniversary Technical Conference, 1975 Reinforced Plastics/Composites Institute, The Society of the Plastics Industry, Inc., Section 17-D, Pages 1 to 4, (b) Belgian Pat. Nos. 828,935 and 828,936, (c) Dutch No. 7505551, (d) West German Nos. 2520819 and 2520820, (e) Japanese No. 43-223, and (f) U.S. Pat. Nos. 3,991,013 and 3,991,014.
It is an object of the present invention to provide an improved melt processable wholly aromatic polyester which is free of ring substitution and which is particularly suited for fiber formation.
It is an object of the present invention to provide an improved melt processable aromatic polyester capable of forming a thermotropic melt phase at a temperature below approximately 300.degree. C. preferably below approximately 280.degree. C. even in the absence of ring substitution which readily may undergo melt extrusion.
It is an object of the present invention to provide an improved wholly aromatic polyester which exhibits a melting point well below its decomposition temperature and which may form with ease quality high performance fibers.
It is an object of the present invention to provide improved wholly aromatic polyester fibers.
It is an object of the present invention to provide wholly aromatic polyester fibers (as defined) which exhibit a high tensile strength and a high tensile modulus which are retained at elevated temperatures while also exhibiting a very low shrinkage propensity and good hydrolytic stability.
These and other objects, as well as the scope, nature and utilization of the invention will be apparent from the following detailed description.
In commonly assigned U.S. Ser. No. 686,189, filed May 13, 1976, by Gordon W. Calundann entitled "Improved Melt Processable Thermotropic Wholly Aromatic Polyester and Process for Its Production" is claimed a generic invention which is free of ring substitution wherein wholly aromatic polyester consists essentially of recurring units of p-oxybenzoyl moiety, 2,6-dicarboxynaphthalene moiety, and symmetrical dioxy aryl moiety.